The present invention relates to a method and apparatus for providing a hydraulic suspension assembly. The hydraulic suspension assembly is particularly contemplated for regulating movement of a vehicle seat in response to vertical travel of the vehicle occurring, for example, when the vehicle is operating over uneven terrain.
The method and apparatus of the present invention more broadly provide hydraulic stabilization in a suspension assembly for supporting a spring mass relative to an unsprung mass.
Many existing suspension systems provide a nearly constant spring rate by means of either a mechanical or fluid suspension linkage. Suspension systems of this type may be undesirable in certain applications such as on earthmoving machines, for example, where the vehicle may operate over very different types of terrain, including both very rough off-highway travel and relatively smooth on-highway operation. One disadvantage for such systems is that the stabilizing force imposed upon a suspended or spring element such as an operator seat is much greater when the vehicle is traveling over rough terrain as compared to situations where the vehicle is traveling over relatively smooth terrain. This comparison exists because the response of the suspension system is generally proportional to the amount of vertical travel encountered or experienced by the vehicle or unsprung mass.
Hydraulic suspension assemblies are also known in the prior art which respond to acceleration forces developed during vertical travel of the vehicle. Such systems may provide a variable spring rate or response for overcoming problems such as those noted above. Hydraulic suspension units of this type are described for example, in U.S. Pat. Nos. 3,492,013; 3,095,214; and 3,300,203; the last noted patent being assigned to the assignee of the present invention.